I've purchased a new, much better fitting saddle for my lease QH (my old saddle was a 7"gullet, this one is 5"), and because it was still sitting a touch low, I bought a solid gel full riser which makes the saddle fit almost perfectly.
When I unsaddle, the area that is equivalent to where the riser sits is noticably less sweaty than the rest. The spine stays dry, so fit is fine in that respect. These 'dry spots' aren't actually dry - they are moist to the touch and the hair is a darker 'wet' shade than normal. My only thought as to why this might be has to do with my weight. I'm definitely a heavy rider; could the pressure from my weight be what causes this 'ill-fit'? The 'dry patches' do correlate with where my weight would be distributed, so it does make sense, in my mind.
For what it's worth, my horse never shows any signs of discomfort before, during, or after riding and performs just as well if not better with me on board than with a lighter rider.
As for 'get a saddle fitter' - I do plan to in the future, if this horse turns out to be a long term investment. He is notoriously hard to fit, and I do know that last time he was fitted he still needed two saddle pads and a riser. Once my bank account refills a little (down due to non horse related vet bills and horse related feeding woes) and I get my car registration out of the way, I'm definitely thinking about getting a fitter out and possibly purchasing a saddle with a changeable gullet.